Smithsonian National Zoological Park l Friends of the National Zoo



Hormone Central

For scientists at the Zoo's endocrinology lab, hormones are clues to solving mysteries of animal life and reproduction.

By Cristina Santiestevan

cheetah cubs

The Zoo's endocrinology lab has helped unlock many of the mysteries of coaxing captive cheetahs to reproduce. (Mehgan Murphy/NZP)

Nicole Presley keeps a baby album on her computer. But her collection isn’t personal. It’s professional. It’s filled with images of zoo babies from around the country. Her collection includes photos of giant anteaters, Asian elephants, and wild muskoxen. A pair of cheetah cubs should look awfully familiar to fans of the Smithsonian’s National Zoo. “These are our guys,” explains Presley.

Presley is the lab manager for the endocrinology lab, located at the Zoo’s Smithsonian Conservation Biology Institute (SCBI) in Front Royal, Virginia. She is one of about a dozen staff members and interns who decipher biological samples for hormonal clues about zoo animals and their wild counterparts.

“Even though all we ever see is their poop or their urine or their serum, we feel like we’re part of all that stuff,” explains Janine Brown, who heads the endocrinology lab. Although they rarely interact directly with the Zoo’s animals, the people who work in this lab play a vital role in understanding the biology of many of the world’s most endangered species.

Shedding Light on Pallas' Cats

“Hormones make the world go round,” says Steve Monfort, director of SCBI and founder of the endocrinology lab. Testosterone, estrogen, norepinephrine (more commonly known as adrenaline), and insulin are just a few of the hormones that affect animal behavior, growth, reproduction, and health. Hormones influence every organ in the body and affect many biological processes, such as heart rate, digestion, and pregnancy. Endocrinology is simply the study of hormones and the endocrine (hormoneregulating) system in the body.

SCBI endocrinologists seek to develop an improved understanding of the basic biology of species, often with a goal of enhancing fertility. For example, long-term studies of hormone patterns in giant pandas yielded new methods for pinpointing the precise moment to artificially inseminate Mei Xiang, the Zoo’s female giant panda.

Janine Brown

Scientist Janine Brown takes part in the successful effort to inseminate Shanthi, an Asian elephant. (Jessie Cohen/NZP)

Detailed studies of elephants’ reproductive cycles led to the discovery of a unique hormone pattern—dual spikes in lutenizing hormone. It can be used to predict the best date for artificial insemination. If the procedure is successful, endocrinologists will also help predict the birth date. Pregnant elephants experience a dramatic drop in progestagen levels three to five days before birth. Because elephants have a 22-month pregnancy, this hormonal clue is extremely helpful for keepers and veterinarians as they prepare for the birth.

Often, however, endocrinology helps solve a mystery. “You want offspring, and you’re not getting them, and you don’t know why,” says Monfort. “The only thing you know is they are not reproducing. Are they conceiving? Are they aborting? Is there a pregnancy loss along the way? Do they cycle normally?”

These are questions that hormones can help answer. Estrogen levels rise and fall as females cycle through normal periods of fertility. Progesterone indicates pregnancy in many species. Abnormal levels of these hormones may point to a non-cycling female or a pregnancy that has miscarried.

Abnormal hormone levels don’t provide a final answer, but they do offer essential clues for solving reproductive challenges with zoo animals. When the Cincinnati Zoo had trouble breeding its Pallas’ cats—small, Siberian wildcats—a hormone analysis by the SCBI’s endocrinology lab helped identify the problem. The cats’ timing was off. The female Pallas’ cats showed a clear spike in estrogen—an indication of breeding readiness—in November, and then a disorganized cluster of peaks later in February.

In contrast, the male’s androgen levels did not peak until late March. That means he was not producing large quantities of sperm when the females were most receptive. The Cincinnati cats were completely out of sync with one another and with Pallas’ cats at other zoos, which consistently show peaking levels of estrogen and androgen in February.

Brown was puzzled by the findings. “I remember calling the zoo and talking to the guy and saying ‘I don’t understand this. Is there anything going on in November?’ And he says ‘Oh. Oh… We have a Festival of Lights, where we turn all the lights on in the zoo for several weeks in November.’” And that was the problem. In the wild, Pallas’ cats begin breeding in early spring, as day length increases. The Cincinnati Zoo’s lights were triggering an early breeding season in the females, but the festival did not last long enough to stimulate sperm production in the male. “They had been trying to breed their cats for years, and didn’t have any luck,” says Brown, “The following year they moved the cats to the other side of the zoo, away from the lights, and they had kittens for the first time.”

These are the happy endings that Brown and others strive for at the Zoo’s endocrinology lab. Although the animals cannot speak for themselves, their hormones can and often do. “Simple, serendipitous, accidental discovery. It completely changes how you manage this species,” says Brown, of the Pallas’ cats hormonal response to the Festival of Lights. “We would never have seen this without hormones.”

Global Resource

In 1986, when Monfort founded the lab in an empty room of the newly constructed veterinary building on the Front Royal campus, endocrinology work was limited primarily to urine samples from primates. Biologists were only just beginning to discover the power of hormonal analysis in wild and zoo animals.

In the 25 years since it was founded, the lab’s work has expanded to include about 80 species of mammals and birds. Urine samples are still frequently used, but samples of feces, blood, hair, and saliva are also important.

And scientists no longer limit their analyses to reproductive hormones. Stress hormones, such as cortisol, are playing an increasingly important role in studies of zoo animals and their wild counterparts.

Despite the progress, there is still much to be learned. Monfort is quick to point out that the 80 or so species they’ve already studied are just a small fraction of the approximately 5,400 mammal species and 10,000 bird species in the world. “The work that we’re doing is very, very rudimentary still, even today.”

Janine Brown

Janine Brown heads the endocrinology lab at SCBI Front Royal. (Jessie Cohen/NZP)

“We know so little about the majority of animals on the planet,” agrees Brown, who explains that increasing our knowledge often starts with questions that can be answered with hormonal analyses. “Is reproduction seasonal? What is the length of the estrous cycle? What is the length of a pregnancy?” By collecting and analyzing samples from a number of individuals, endocrinologists are able to begin answering these basic questions. From there, biologists build research projects, conservation initiatives, and captive-breeding programs. “We provide information that other people can build on,” says Brown.

The endocrinology lab handles hormone analyses for both zoo-based and field-based research projects throughout the United States and around the world. It is the largest service laboratory for wildlife endocrinology in the world. Frozen samples—blood, urine, feces, saliva, or hair—are shipped overnight from all over the globe. One researcher ships muskox feces from the Arctic. The U.S. Fish and Wildlife Service ships elk feces from Yellowstone. And, in preparation for a recent Asian elephant birth, the Houston Zoo shipped samples from its expectant female every single day.

“It’s a win-win for everyone,” explains Brown. “The facilities get the information they need so that they can work on the management of their species. And then we get the benefit of having a huge database of reproductive information on a whole variety of species that we would never be able to get otherwise.” That database ultimately helps answer questions about the care and reproduction of zoo animals. It was this kind of information gathering that allowed Brown to spot the unusual reproductive cycle in Cincinnati’s Pallas’ cats.

But the laboratory cannot possibly handle all the necessary hormone analyses for the world’s zoos and wildlife research projects. We don’t have the capacity to possibly do enough,” says Monfort, who explains that there is just too much left to learn—too many species that haven’t been studied, too many questions that haven’t been answered. “While we have a big lab, it’s not enough. There ought to be a hundred labs like us to have a shot at making a dent in what we don’t know.”

The world may be a long way from having a hundred labs like SCBI’s, but Brown and her colleagues are actively training the next generation of wildlife endocrinologists. The laboratory hosts both undergraduate and graduate-level interns, as well as pre-veterinary students. In a typical semester, about six to eight students walk these halls and learn from SCBI’s wildlife endocrinology staff.

All told, the lab is easily Earth’s largest training facility for wildlife endocrinology. Beyond training individuals, the Zoo also helps launch endocrinology labs in other countries: three labs in Thailand, one in Australia, one in New Zealand and one in Sri Lanka. “We’ve got people everywhere,” says Brown, who estimates that hundreds of students have passed through the Zoo’s endocrinology lab. “I think it’s because the atmosphere here is to give back. We put as much effort into giving out as we do into doing our own internal thing.”

Team inseminating Mei Xiang

An international team works to artificially inseminate Mei Xiang, the Zoo's female giant panda. (Mehgan Murphy/NZP)

The "Happiness" Hormone

The cheetah cubs on Presley’s computer are an example of another mystery solved by the endocrinology lab. In 1999, the Zoo initiated a breeding program with the cheetahs on display in D.C. The cats were healthy, and the exhibit was specially designed as a breeding facility. But no cubs arrived. Why not?

Endocrinology provided the first clue. The female cats were “flat-liners,” meaning that their estrogen levels were not peaking in the regular cycle that is normal for cheetahs. Something had shut down their estrogen production. As a result, the female cheetahs’ ovaries were inactive. The endocrinology lab results revealed the problem— non-cycling females—but not the cause.

The answer became clearer when Brown compared hormone analyses of solitary female cheetahs with group-living females. Those females who were living with other female cheetahs weren’t cycling. But the solitary females were. A review of wild cheetah behavior confirmed that female cheetahs are solitary creatures. They interact with others of their kind only when breeding or raising their cubs. When housed with other females in zoos, the cheetahs stopped reproducing. Once separated, the cats began to cycle again. And zoos began celebrating cheetah births.

Asian elephants

The Zoo's endocrinology lab monitors the hormone levels of elephants across the country. (Mehgan Murphy/NZP)

Brown hopes that similar discoveries await elephants in the next few years. The National Zoo is one of seven partners collaborating in a three-year study on elephant welfare. It will look at nearly 290 Asian and African elephants in approximately 70 zoos throughout the United States. The SCBI endocrinology lab will be analyzing blood, feces, and saliva for hormonal clues into elephant behavior, growth, health, and reproduction.

The lab will also attempt to measure elephants’ “happiness.” Endocrinologists know that hormones such as oxytocin and prolactin are indicators of well-being or contentedness in humans. This project will be the very first time that anyone has attempted to measure these happiness hormones in wildlife or zoo animals. The results of these tests will help identify who is “happy” among the American elephant population. This will provide vital clues for biologists and zoo keepers as they strive to develop new policies and facilities for elephants around the world.

“We think that this welfare project could be a model for any number of other species,” says Brown, who is excited about the broad scope of the study. No previous study has looked so holistically at the well-being of a single species. Similar large-scale welfare projects may be launched for other species in the coming years. The results could change—for the better—how zoos care for their animals. Ultimately, studies such as these could also give Presley more photos for her digital album of zoo babies.

Freelance writer CRISTINA SANTIESTEVAN last wrote about the Zoo's pathology lab.


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Smithsonian Zoogoer 40(3) 2011. Copyright 2011 Friends of the National Zoo. All rights reserved.